In early cam operated drive trains, the effects of right angle forces were ignored. For example, Handwerker U.S. Pat. No. 1,792,836 discloses a cam operated drive train for a valve mechanism using a simple connection between rocker arm 19 and valve stem 14. In this system, no push rod is used and the rocker arm directly contacts the top of the valve stem. The end of the rocker arm contacting the valve stem is rounded and its contact portion on the valve stem is flat. The valve stem translates and this translation is caused by the rotation of the rocker arm. However, there is no intermediate element to efficiently convert the rotational motion of the rocker arm to the translational motion of the valve stem. The rotation of the rocker arm over the relatively short distance that the valve stem translates is theoretically approximated by a straight line. However, in practice, this approximation ignores the significant sideways loads and thrusts imposed on the valve stem. Furthermore, eventually, the rounded end of the rocker arm could wear away the top of the valve stem in a concave fashion. This concavity could cause the sideways loads on the valve to still further increase tremendously.
While the increased wear caused by the side loads induced by the drive train illustrated in Handwerker could possibly be tolerated in a valve guide, such an approach could lead to very early and costly malfunction of a unit fuel injector.
One partial solution to the side loading problem presented by Handwerker-type systems has been to use a push rod as the link between the rocker arm and the lower plunger of the injector plunger. This approach reduces much of the frictional sliding contact inherent in the Handwerker-type drive train. In cam operated unit fuel injectors using push rod links, the injector typically includes an injector plunger mounted for reciprocal movement within a bore of the injector body. Reciprocal movement of the plunger is induced by a rotating cam operating through the injector drive train typically including a cam follower connected to one end of a connecting rod which is in turn connected at its other end to a rocker arm. The rocker arm is rotatably mounted on a pivot disposed in a central portion of the rocker arm. At one end the rocker arm is connected to the connecting rod and at the other end, on the opposite side of the pivot, the rocker arm is connected to a push rod. The push rod is, in turn, connected to the injector plunger. Thus, as the cam on the camshaft rotates, the cam follower and connecting rod reciprocate. This reciprocation rotationally oscillates the rocker arm around its pivot to cause the push rod to reciprocate, and therefore the plunger to reciprocate, in the direction opposite that of the cam follower and connecting rod.
Two examples of fuel injectors using this type of drive train connection system are disclosed in Perr, U.S. Pat. No. 3,965,875 and Reiners, U.S. Pat. No. 3,544,008, both of which are commonly assigned to the assignee of the present invention, Cummins Engine Company, Inc. As illustrated in these patents, (reference will be made to FIG. 2 of the '008 patent for clarity) the injector plunger actually is formed of two separate but connected components, a lower plunger 37 which translates within the injection chamber and an upper plunger or sleeve portion 72 which extends from the lower plunger to the upper ends of the plunger body. The upper plunger is hollow along substantially its entire length to receive a push rod, link 29 which contacts the rocker arm at its upper end. The lower end 83 of the push rod is spherically formed and is received in a complementarily shaped seat 84 in the inner lower end of the upper plunger.
The reciprocating movement of the push rod is only approximately linear due to the rotation of the rocker arm. Therefore, the push rod receives a force component at right angles to the desired direction of translation. The magnitude of the right angle forces on the plunger will vary with the particular drive train design but such right angle forces can lead to extreme wear in the surfaces of the plunger and the mating surfaces of the injector body bore in which the plunger is received.
As illustrated in the '875 and '008 patents, additional improvement can be achieved by elongating the push rod a substantial distance into the injector body axial bore which receives the plunger. By lengthening the push rod, the reciprocal movement of the push rod will become more nearly linear thereby minimizing the laterally directed force on the plunger. However, these systems result in high levels of wear at the socket between the push rod and the plunger, at the top of the lower plunger disposed in the injection chamber. Additionally, there still remains a significant sideways force component which causes further wear on the injector plunger and plunger bore which can result in excessive fuel leakage and a loss of control over the amount of fuel injected per injection stroke. This is a very serious limitation with fuel injectors because the precise and accurate control of fuel metered into the combustion chamber through the fuel injector is critical to efficient proper performance of the engine.
Leblanc et al., U.S. Pat. No. 4,571,161, is directed to a fuel injector having a socket for receiving a drive train push rod located at the upper portions of the plunger assembly near the top of the injector body. In this configuration, the side loading on the plunger adjacent the injection chamber is removed and is applied to the sliding tappet 19 mounted on plunger 17. However, this results in increasing the load on the tappet socket. Also, because of the configuration of the fuel injector, the size of the socket connection is constrained because the socket is located within a portion of the tappet that is located entirely within the inner diameter of the return spring. This causes the contact surface between the end of a push rod and the tappet to be disposed totally below the upper end of the return spring.
A drive train configuration similar to Handwerker's but applied to the actuation of a fuel injector is found in Truxell, Jr. U.S. Pat. No. 2,144,861 in which ball ended member 27 formed on one end of rocker arm 24 is disposed within block 26 disposed on top of plunger follower 21. In Truxell, the block is free to slide horizontally on plunger follower 21 thereby avoiding some of the disadvantages of the Handwerker mechanism but still creating and transmitting sideways loads on the plunger follower and on the injector as a whole.
In Maddalozzo, U.S. Pat. No. 3,409,225 another prior art plunger-driving assembly connection is shown. Rocker 52 is connected to the upper portion of plunger assembly 18 through slipper 56 which is the sole link between the injector plunger assembly and the rocker arm. Slipper 56 has an indentation for receiving a downward projection of rocker arm 52. The precise relationship of slipper 56 and cup 26 is not disclosed. Moreover, Maddalozzo et al. fails to disclose a push rod between the rocker arm and the plunger assembly.
Although spherical connections between the push rod and plunger located near the outer surface of the plunger and outside of the injector housing bore have been employed, heretofore there has been no simple connection which reduces almost to elimination the sideways stresses on the fuel injector to reduce plunger wear at the connection and maintain control over fuel injection.